7G JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



It may be noted that a tendency to elongate the axis prevail* 

 in plants grown under yellow as under red glass, and to a less 

 extent under green. They thus resemble plants grown in totai 

 darkness and with a sufficient temperature. This clearly in- 

 dicates the necessity of the presence of the more refractive rays 

 of the spectrum to ensure normal growth. On the other hand, 

 a most important difference exists, in that while plants grown in 

 the dark are etiolated, those grown under coloured glasses are ali 

 pretty equally green, and therefore capable of assimilating carbon- 

 dioxide, though it may be in very different degrees. This elon- 

 gation of the stems, which decreases from the red to the blue 

 glass, is possibly due in part to the confined air becoming more 

 saturated with moisture under red, yellow, and green, as the 

 heat-rays are of course greater and tend to saturate the air ; sa 

 that in this respect the elongation of the stems, as takes place in 

 etiolation, would confirm Vesque's and Yiet's researches, who 

 found that a too moist atmosphere produced much the same 

 effects on the growth of plants as obscurity.* 



With regard to the comparative effects of yellow and blue- 

 glasses, we find that of the total weights given in Table I. (1), the 

 plants under yellow glass gained weight at a higher ratio, or 

 as 435 per cent, to 249 per cent, for blue, the total weights 

 being as 43-5 grs. under yellow and only 24'9 grs. under blue 

 glass. Similarly the total amount of dry substance is greater 

 under yellow than under blue glass (Table II. col. 1). 



When, however, the amounts of dry substance are reduced 

 to percentages (Table II. col. 4), that under blue (10*6) is greater 

 than that under yellow (7*3), and comparing the second and third 

 columns with the sixth of Table II. we see that while under yellow 

 the total amount showed a deficiency whether compared with the 

 initial or final stages of growth, there was a gain under blue in 

 the first case, but a slightly larger deficiency in the second. 



These results show that while yellow light favours the assimi- 

 lative process so far as quantity represented by the total weight 

 (i.e. of dry substance and water together) is concerned, as well as by 

 the calculated total weight of dry substance alone (Table II. col. 1), 

 blue light favours assimilation strongly as well, in causing even a 

 larger 11 storage" (as shown by the percentage of dry substance) 



* Ann. dc I'Jnst. Nat. Agro. 8* ann., et Ann. Sc. Nat. 0' s£r. t. xiii.. 

 p. 1G7. 



